Magnesium silicate electrical insulating composition



Patented Dec. 1, 1936- UNITED STATES MAGNESIUM smears: ELECTRICAL INSULATING COMPOSITION Edgar Kunstmann, Berlin-Heinersdorf,

assignor to Steatit- Magnesia Aktiengeselb' schaft, Berlln-Pankow, Germany No Drawing. Application October 4, 1933, Serial No. 692,145. In Germany February 21, 1933 13 Claims.

The invention relates to a method of reducing the dielectric loss of magnesium silicate masses.

Insulating parts consisting of'porcelain and similar ceramic substances disclose high dielectric losses. Pure quartz glass and mica are practically free from loss but are not adapted for many uses where insulators are required. On the other hand, magnesium silicate masses produced from ground soapstone or talc, the so-called steatite masses can be used in almost any shape or place. Compared with other common ceramic substances,- steatite discloses. already a very lbw dielectric loss, but nevertheless sufllclent loss to be objectionable to electrical engineering.

The invention makes it possible to reduce the dielectric loss of magnesium silicate masses of the kind mentioned still more, and in connection therewith to obtain other advantages of great importance.

ramic purposes contains generally from 70% to 90% of soapstone or talc. During burning, re-

crystallization and new crystallized compounds dielectric loss. In order to, reduce the dielectric loss, it has been discovered that it is necessary to obtain a mass having throughout a crystalline lo structure with no appreciable, and preferablyno visible, glass between the crystals, and relatively large crystals are desirable. In order to accomplish this result, it has been found desirable to greatly reduce the amount of clay which has been and to employ, instead of alkaline fluxes which produce glass, alkaline earth fluxes, the alkaline earth compounds preferably comprising at least 60% of the material in the batch other than 50 steatite with the clay constituting not over 40% of the batch other than steatite. All oxides of the alkaline earths ranging from beryllium to barium may serve'as alkaline-earth fluxes. A

mass 'of specialdielectric .quality is obtained by 55 introducing simultaneously two or more. alkaline Raw steatite material normally used for ce- 1 massesis generally employed in forming a steatite batch earths, e. g. calcium and barium compounds. Barium oxide will combine at diiferent proportions with silicic acid and these combinations, like many barium compounds, possess an extraordinary capacity to crystallize. These barium 5 silicates are capable of forming, with other alkaline earths, such as calcium silicates, in any proportion, mixed crystals and solid solutions.

A steatite mass according to the inventionv shows at 30 m. wavelength 9. power factor (cos 3!), of less than 410*, i. e., a value approaching directly that of molten quartz, while the corre sponding values of normal steatite masses built up with an ample amount of clay substance are at cos 1 equal to about 8 15.10- The dielectric constant of the new steatite mass is approximately' 6. Owing to their crystalline character, the mechanical strength of masses produced according to the invention is very} great. measurements carried out with the 10 cm/kg Schopper hammer onrods having a length of 120 and a cross section of 12 cm disclosing a value of more than 4 cm/kg/cm.

There are steatite masses known already which contain both calcium oxide and aluminium oxide as sintering agents. The CsO/AlzOs/SiOz system, as is generally known, forms, however, a large number of eutectic mixtures and .thus leads to the production of an ample amount of melt and, during solidification, of glassy portions which are avoided by the invention. The same applies to the use of any flux which results in a considerable amount of glass.

Of special importance is the possibility afforded by a special application of the new method of influencing the dielectric loss factor of ceramic bodies of the kind described in such a way that it varies considerably in the same sense as the wavelength and for this reason the bodies produced according to the invention will disclose, especially in the short-wave sphere where the losses are most troublesome, an extraordinarily low dielectric loss. Y

The dielectric loss factor of such ceramic bodies is more or less dependent on frequency, and masses are known whose dielectric loss factor varies in the same sense as the wave-length or in the opposite sense.

In the first-mentioned insulating bodies of known kind the reduction of the dielectric loss' is not efl'ected quickly enough with decreasing wavelength to satisfy the requirements of broadcasting engineering, particularly with respect to short waves say of 6 m. and less.

A surprising result is attained in this respect acso 'oi material in th glass phase.

cording to the invention it in preparing the mass as described barium oxide is introduced as al A Magnesium silicate mass without barium oxide content e h 150 6 iiitiiittihfti:

Power factor. 9.6 9. 8.5 7.5 25%.

man

3 Magnesium silicate mm with barium oxide content wavelength so) 150 is as o figff f fia? Powar iactor as 5.5 4.3 3.3 as 51%.

one '10.

Th fundamental idea of the inventionand the main condition for its tuccessiulapplication can be summed up by stating that in masses'oi the kind described theiorination of 'glassyconstitu ants should be prevented as much as possible and a coarsely crystalline structure of crystals, as

tree as possiblairom glass, produced-1mm magnesium'and o her alkal ne earth In the appended clainis the term-clay is intended to cover'the broad class 0! materials asindicated in the foregoing description.

1. in insulating material consistin of. from rod, :to 90% magn sium siiicate nnd the; re-

mainder chiefly of alkaline earth metal )oxide :compoundsland clamflred together, thealkaline earth metal c'orn'p'c'nirid, calculated as oxide, constituting at least 60% 9f'said'jem8 n er.

- 2. An insulating material in accordance with claim 1, of crystals free from a detectable amount 3. An insulating material in accordance with claim 1, and in which-said oxide is of more than "one alkaline earth metals.

4. An insulating material in accordance with claim 1, and in which said oxide includes barium Oxldfi;

5. An insulating material in accordance with claim 1, and in which said oxide consists oi barium oxide.

6. An insulating material consisting oil from 70% to 90% magnesium silicate and a remainder consisting chiefly of alkaline earth metal oxide compounds and clay, the alkaline earth compound, calculated as oxide constituting at least 60% of said remainder, and all of said ingredlents fired together to a crystalline phase.

'1. An insulating material consisting of 70% to 90% magnesium silicate and the remainder of calcium compound, barium compound and clay, 'the'alkaline earth compounds, calculated as oxides, constituting at least 60% of said remainder,

and allot said ingredients fired together to a crystalline phase.

' 8. An insulating material consisting of 70% to I 90% magnesium silicate, and barium compounds,

calculated as oxide, constituting at least 60% 0! the remainder, all of said ingredients being fired together to a crystalline phase.

9. An insulating material consisting of 70% to 90% magnesium silicate and the remainder barium oxide, fired toge'ther to a crystalline phase.

10. 'An insulating material consisting of 70% to 90% magnesium silicate and the remainder consisting chiefly oi alkaline earth metal compounds and clay, the amount of alkaline earth compounds calculated as oxides being at least 50% greater than the amount oi clay, and said materials being fired together to the crystalline phase.

7 llfiAn insulating material consisting of 70% to 90% magnesium silicate and a remainder containing'barium oxide fired together to a crystalline these. i v

Q12. An insulating material consisting 01' 70% to 90% magnesium silicate and a remainder containing barium oxide and clay fired together to a crystalline phase.

.13. An insulating material consisting of 70% to ;gn .magnesium silicate and a remainder. containing barium oxide the barium compounds calculated as oxide constituting at least 60% of the remainder all of said ingredients being fired togethcr to a crystalline phase.

EDGAR KUNSTMANN. 

